US President Donald Trump said on Saturday he hoped to play golf at his course in Scotland ahead of a summit with Kremlin chief Vladimir Putin that could be overshadowed by accusations that Russians meddled in the US 2016 election.

In an uproarious trip to Europe, Trump harangued members of the NATO military alliance, scolded Germany for its dependence on Russian energy and shocked Britain by publicly criticising Prime Minister Theresa May's Brexit strategy.

Trump apologised to May for the furore over his withering public critique, blaming "fake news" and promising instead a bilateral trade agreement with Britain after it leaves the European Union in March.

While Trump took tea with Queen Elizabeth, a U.S. federal grand jury charged 12 Russian intelligence officers with stealing data from the campaign of Democratic presidential candidate Hillary Clinton.

Trump has repeatedly said the investigation into suspected Russian interference in the 2016 U.S. election - which he casts as a "rigged witch hunt" - makes it hard for him to do substantive deals with Moscow.

After meeting the queen at Windsor Castle, Trump headed to Scotland, where his mother, Mary Anne, was born and where he owns a golf course, before his meeting in Helsinki with Putin.

"Will be at Trump Turnberry for two days of meetings, calls and hopefully, some golf - my primary form of exercise!" Trump said on Twitter. "The weather is beautiful, and this place is incredible! Tomorrow I go to Helsinki for a Monday meeting with Vladimir Putin."

While at his Turnberry course on Friday evening, an activist for the Greenpeace environmental campaign group swooped on a powered parachute within a few hundred yards of the president as he stood outside the golf course's hotel.

Trump moved calmly inside as the parachute approached, surrounded by his security detail. British police said they were trying to trace the pilot.

After tens of thousands of people marched peacefully against Trump in central London, more protests are planned on Saturday. A blimp depicting Trump as an orange, snarling nappy-wearing baby was due to be raised at a park in the Scottish capital.

"I'm here as a quiet protestor to say: I really don't want this man in our country," said Graham Creelman, 70, who joined a small protest on the beach beside the Turnberry golf course.

"The government needs to take a stand against appalling attitudes and appalling behaviour, and we're not doing it."

British Trade Secretary Liam Fox said anti-Trump protesters were an embarrassment to themselves as they had shown bad manners to the leader of the free world.

Around 100 supporters of Trump, some wearing "Make Britain Great Again" hats, expressed their admiration for the president opposite the U.S. embassy in London.

DONALD AND VLADIMIR

Trump and Putin, who control the world's two biggest nuclear arsenals, are due to meet in the Finnish capital, a venue that evokes memories of Cold War showdowns between the Soviet Union and the United States.

In the most detailed US accusation to date that Moscow meddled in the presidential election, a federal grand jury said Russian military intelligence agency officers covertly monitored computers of Clinton's campaign and Democratic campaign committees, and stole large amounts of data.

The charges shine an even greater spotlight on Trump's treatment of Putin, who has repeatedly denied Russia sought to intervene or skew the US election that Trump, a Republican, unexpectedly won.

Trump questioned why Barack Obama had not acted on claims of Russian meddling if the FBI had informed the then president ahead of the 2016 election. He also asked where the Democratic National Committee server now was.

When asked at a news conference on Friday whether he would tell Putin to stay out of U.S. elections, Trump said "yes."

The president also indicated he did not expect much progress on the issue. "I will absolutely bring that up," Trump told reporters. "I don’t think you’ll have any 'Gee, I did it. I did it. You got me.'"